Cometary Airbursts and Atmospheric Chemistry

We're interested in the changes made to our atmosphere as a result of
comet or asteroid impacts. Even moderate ones, such as the famous 1908
Tunguska (Russia, Siberian region) airburst can have a measurable effect
on atmospheric chemistry. We have simulated the event and produced
results that agree with ice core data. We then consider a million-times
larger event which may have happened over the North American ice sheet near
the end of the last ice age. The results are interesting--at this point
I believe I will just
link a PowerPoint presentation, which should be
self-explanatory.
Or
pdf in case you prefer that.
For a more formal presentation,
our paper about this
has been published on Geology. An account in
Science News explains the main points.

More recently, Drew Overholt led an investigation into the direct
deposition of cosmogenic isotopes from asteroids and comets.
It appears that interesting amounts of Carbon-14 and
Aluminum-26 can be deposited by larger events.
This may be a strong test of such impact
hypotheses.